Validation of a complex urban noise model close to a road

The adequacy of a model for the sound level close to a road is investigated by comparing resulting predictions for the sound level over a building façade with measurements. The road model involves the road geometry (the number and positions of traffic lanes), the traffic structure (vehicle flow rates and their average speeds in each lane) and equivalent omnidirectional point sources representing the vehicles. It is found that the assumed road traffic noise source model is adequate only for predicting levels over the higher part of the façade. However the investigation has allowed definition of what improvements are needed in the road source modelling to enable adequate predictions over the whole of the building façade.     

Modelling of sound propagation to three-dimensional urban courtyards using the extended fourier PSTD method

Noise from road traffic propagates to acoustically shielded areas as roadside courtyard by multiple reflection and diffraction paths in a complex three-dimensional (3D) environment. The computation of noise levels and assessment of candidate noise mitigation measures for these areas has up to now been based upon two-dimensional (2D) geometrical assumptions. Here, a recently developed efficient wave-based method, the extended Fourier pseudospectral time-domain (PSTD) method, is used to investigate the necessity of a 3D model. For frequencies up to 500 Hz and low traffic velocities of 30 km/h and 50 km/h, a road traffic noise configuration of an urban street canyon with or without cross streets and a closed roadside courtyard is compared to the 2D configuration as studied previously. It can be concluded that the contribution of distant sources is overpredicted by the 2D configuration. As noise mitigation measures, additional façade absorption, façade screens and roof screens have been studied. Results show that the 2D configuration underpredicts the effect of façade mitigation measures, by maximum 1.5 dB(A) for the absorption case and 4.4 dB(A) for the screens case. The effect of roof screens is overpredicted up to 1.7 dB(A). Given these deviations and the found deviations between the 3D configurations of street canyon with and without cross streets, the need for a 3D model can be concluded to be strongly configuration dependent. The 3D model is finally used to investigate the effect of a façade opening to the courtyard, which could lead to up to 10 dB(A) higher noise levels as compared to the noise propagating over the roof level and may prohibit the use of these courtyards as quiet areas. Absorption in the façade opening can significantly limit this negative effect.     

The importance of roof shape for road traffic noise shielding in the urban environment

The influence of roof shape on sound propagation in a densely build-up city centre is evaluated. Road traffic noise propagation from a street canyon to an adjacent, non-directly exposed building façade is numerically studied by the finite-difference time-domain method. A large number of common and less common roof shapes were analyzed in an idealized city canyon configuration. Roof shape can be responsible for differences in road traffic noise shielding exceeding 10 dBA, averaged over the shielded façade. Therefore, roof shape can be considered as an important means to limit sound pressure levels at a quiet side; various researchers indicated that the presence of silent zones and façades may limit city noise annoyance. With increasing vehicle speed, the choice of roof shape becomes more important. The roof top height was shown to be a bad predictor of shielding efficiency in the equal-building-volume approach followed in this study.     

Full scale model investigation on the acoustical protection of a balcony-like façade device (L)

The acoustical insertion losses produced by a balcony-like structure in front of a window are examined experimentally. The results suggest that the balcony ceiling is the most appropriate location for the installation of artificial sound absorption for the purpose of improving the broadband insertion loss, while the side walls are found to be the second best. Results also indicate that the acoustic modes of the balcony opening and the balcony cavity resonance in a direction normal to the window could have a great impact on the one-third octave band insertion losses. The maximum broadband road traffic noise insertion loss achieved is about 7 dB.     

Noise screening effects of balconies on a building facade

The insertion loss and its spectrum due to a rectangular balcony on a building facade in the presence of sound reflection and scattering from adjacent balconies were examined using a scale model. The front panel of the balcony dictates the screening performance, while the side walls of the balcony are found to be insignificant. Balconies without a front panel do not provide acoustic protection in the presence of upper balcony reflection, especially for a distant noise source. Sound amplifications are also observed in many cases. In addition, the shapes of the insertion loss spectra are found to depend on the elevation angle of the balcony. Significant correlations between the A-weighted balcony insertion losses with this angle are found in the absence of upper balcony reflections. With such reflection, an angle defined using the balcony configuration and source position correlates within engineering tolerance to the insertion losses.     

Road traffic noise - the relationship between noise exposure and noise annoyance in Norway

Exposure-effect relationships between the level of road traffic noise at the most exposed side of a dwelling's façade and the residents' reactions to road traffic noise have been estimated. The relationships are based on five Norwegian socio-acoustic studies featuring 18 study areas from two cities and a total of near 4000 respondents. The survey questionnaires distinguish between noise annoyance experienced right outside the apartment and when indoors. Exposure-effect relationships for all degrees of annoyance are estimated simultaneously from ordinal logit models. These predict road traffic noise annoyance when right outside the apartment and when indoors, respectively, as a function of the road traffic noise level outside the most exposed façade. Separate analyses indicate that Norwegians react stronger to road traffic noise than results from a recent compilation of socio-acoustic surveys would lead one to believe. People having inferior single glazing windows report higher indoor annoyance.     

Traffic noise reduction at balconies on a high-rise building façade

The performance of balconies with ceiling-mounted reflectors on a high-rise building fac?ade is examined using numerical analyses and scale-model experiments. The reflectors are designed to reflect direct and diffracted waves incident on the ceiling outside the balcony. The sound pressure reduction, provided by the reflectors, on a window surface adjacent to the balcony is evaluated at intermediate floors levels. In terms of A-weighted sound pressure levels, a balcony equipped with reflectors reduces road traffic noise by 7-10 dB(A), compared to an ordinary balcony, at incident angles of noise close to the angle for which the reflectors are designed. The efficiency is roughly the same as, or greater than, that of a balcony with an absorbent ceiling. However, it is also shown that when the vertical incident angle of the noise is smaller than the design angle of the reflectors, or the horizontal incident angle is large, efficiency is reduced.     

A simple formula for evaluating the acoustic effect of balconies in protecting dwellings against road traffic noise

This study explores the noise reducing effect of a balcony and describes the development of a simple theory pertaining to the propagation of traffic noise from a road into a balcony. A new methodology is proposed that is based on the well-known prediction scheme—“Calculation of Road Traffic Noise” (CRTN)—developed in the UK. A geometrical ray theory is developed for the prediction of noise levels inside a balcony due to road traffic. The source level of road traffic noise is obtained as per the standard CRTN methodology. However, road sub-segmentations and new approaches for the prediction of noise levels at illuminated and shadow zones inside a balcony are proposed. Field measurements have been conducted on four different types of balcony to validate the proposed methodology. The insertion loss, defined as the difference in the noise levels with and without the presence of a balcony, has been used to assess the shielding effectiveness of a balcony against road traffic noise. The simple theory is validated by outdoor field measurements. It is also found that a properly designed balcony can provide considerable screening effects in protecting dwellings against road traffic noise.     

Sound fields near building facades - comparison of finite and semi-infinite reflectors on a rigid ground plane

The sound field in front of, and close to a building facade is relevant to the measurement and prediction of environmental noise and sound insulation. For simplicity it is often assumed that the facade can be treated as a semi-infinite reflector, however in the low-frequency range (50-200 Hz) this is no longer appropriate as the wavelengths are similar or larger than the facade dimensions. Scale model measurements and predictions using integral equation methods have been used to investigate the effect of diffraction on the sound field in front of finite size reflectors. For the situation that is commonly encountered in front of building facades, the results indicate that diffraction effects are only likely to be significant in the low-frequency range (50-200 Hz) when the façade dimensions are less than 5 m. This assumes that there is a point source close to the ground and microphones at a height of 1.2 or 1.5 m, at a distance between 1 and 2 m in front of the façade.     

3D analysis and investigation of traffic noise impact from a new motorway on building and surrounding area

This study analyzes and investigates the impact of traffic noise on the high-rise building and surrounding area by the side of a new motorway that links Bangkok to the new Suwannaphum International Airport and Pattaya. A traffic noise simulation model in 3D form is applied on a GIS system. Visualized noise levels are formulated in vectored contours for noise mapping on all surfaces of the building and surrounding ground in a 3D platform. Noise impact is then investigated based on this 3D noise mapping in LAeq,1 h noise contours. The investigation shows that there is a high traffic noise impact on the foreground and front façade of the building, rendering this area unsuitable for residential purposes. The ground area by the sides of the building and the building side panels receive a lower noise impact. Most of these areas are still not acceptable for residential use; however, all of the side panels and most of the ground area by the sides of the building can be used for commercial and business purposes. The back yard and back panel, together with the rooftop, have the lowest traffic noise impact. They are the safest places for use as residential areas, except for a small strip along the front edge of the rooftop. From this study, residential areas that are sensitive to noise impact must be located far away from the front façade and side panels of a building. It is also shows that the building height is not an effective means of reducing motorway noise on the upper part of the building.     

Parameter study of sound propagation between city canyons with a coupled FDTD-PE model

A parameter study is performed for the case of two-dimensional sound propagation from a (source) city canyon to a nearby, identical (receiver) city canyon. Focus was on sound pressure levels, relative to the free field, in the shielded canyon. An accurate and efficient coupled FDTD-PE model was applied, exploiting symmetry of the source and receiver canyon. With the proposed calculation method, simulations were necessary in only half the sound propagation domain. The shielding in the receiver canyon in case of a coherent line source was compared to the shielding by an incoherent line source, by means of sound propagation calculations in a number of 2D cross-sections through source and receiver. It was found that the shielding is rather insensitive to the width-height ratio of the canyons. The presence of diffusely reflecting façades and balconies lead to an important increase in shielding compared to flat façades. Rigid façades yield significantly lower shielding compared to partly reflecting façades. Effects of a moving atmosphere were modeled in detail. Shielding decreases significantly in case of downwind sound propagation when comparing to sound propagation in a non-moving atmosphere. Refraction is the most important effect in the latter. In case of upwind sound propagation, turbulent scattering plays an important role and the shielding is similar to the one of a non-moving atmosphere for the parameters used in this paper. The combination of effects, as is shown by some examples, is in general not a simple addition of the separate effects.     

A scale model investigation of sound reflection from building façades

A simple model for predicting the sound reflected from a building façade is developed based upon the assumption that the scattering coefficient is small. This model is then used as the basis of an experimental attempt to measure the scattering properties of scale model façades featuring a similar degree of surface irregularity to that found on real buildings. A series of measurements made on a simple scale model are described and the effect of a non-uniform distribution of façade scattering is examined. The measured value of the scattering coefficient is found to be small and not very sensitive to the degree of surface irregularity. A progression of energy from a specular reflection field to a diffuse reflection field for successive orders of reflections is observed. It is suggested that the dominant mechanism of sound propagation for higher order reflections is via random scattering and that the development of propagation models based upon purely random scattering is a valid approach.     

Simulating the effect of acoustic treatment types for residential balconies with road traffic noise

Development of design guides to estimate the difference in speech interference level due to road traffic noise between a reference position and balcony position or façade position is explored. A previously established and validated theoretical model incorporating direct, specular and diffuse reflection paths is used to create a database of results across a large number of scenarios. Nine balcony types with variable acoustic treatments are assessed to provide acoustic design guidance on optimised selection of balcony acoustic treatments based on location and street type. In total, the results database contains 9720 scenarios on which multivariate linear regression is conducted in order to derive an appropriate design guide equation. The best fit regression derived is a multivariable linear equation including modified exponential equations on each of nine deciding variables, (1) diffraction path difference, (2) ratio of total specular energy to direct energy, (3) distance loss between reference position and receiver position, (4) distance from source to balcony façade, (5) height of balcony floor above street, (6) balcony depth, (7) height of opposite buildings, (8) diffusion coefficient of buildings and (9) balcony average absorption. Overall, the regression correlation coefficient, R², is 0.89 with 95% confidence standard error of ±3.4 dB.     

How the money machine may help to reduce railway noise in Europe

The need to reduce railway noise, particularly from freight transport in international traffic, is recognized by all stakeholders in the field. Solutions are currently available to provide a significant reduction, and research is underway to investigate further options. Several recent studies clearly show that noise abatement at the source (i.e., vehicles and track) are to be preferred over solutions that affect noise propagation (e.g., barriers) or noise reception (façade insulation) when it comes to overall life cycle cost. In spite of these three important conclusions, the necessary noise reduction at source is not yet taking place, with some small-scale exceptions. The parties involved agree that financial and economical constraints prevent the process of noise reduction from starting. The present paper presents the results of the second consensus building workshop in the STAIRRS project. It explores the possible financial and economic instruments that may help to launch the necessary developments.     

Testing the acoustical corrections for reflections on a façade

The assessment of noise levels, in the proximity of a building or on its façade, is a requirement of the European Environmental Noise Directive 2002/49/EC concerning environmental noise produced by road and railway traffic, airports and industries. The corrected values for the noise levels and the problems of measuring noise near a façade are discussed here for the case of road traffic. A complete set of measurements in different situations was performed along several roads in an urban environment as well as in a controlled situation using a loudspeaker. The experimental results are then compared against theoretical models and international standards, in particular those that suggest to use a +3 or +6 dB correction as a function of the microphone position and the NordTest method. Some suggestions are given for the different corrective factors to apply when measuring environmental noise between 0 and 2 m away from a building façade, and practical solutions identified.     

高层住宅阳台降噪量的计算分析

高层住宅中的阳台不仅具有居住及建筑上的功能,对道路交通噪声也有衰减作用。本文通过建立噪声传播模型计算高层住宅阳台的插入损失,并探讨了影响阳台降噪量的一些因素。同时对阳台内部吸声处理的效果进行了理论预测。     

Prediction of the sound field into high-rise building facades due to its balcony ceiling form

This study presents the acoustic performance off tall building facades closed to roadway due to one of balcony configurations, namely ceiling, with an inclined form in terms of traffic noise reduction. Three inclined angles are tested (5,10, and 15°) with different balcony depths by using a Pyramid Tracing model developed by A. Farina. The results in terms of A-weighted sound pressure level reduction are expressed in free field into the balcony back wall. The protection level, defined as the difference in noise levels before and after inserting the proposed balcony form, has been used to assess the reduction offered by that configuration. A maximum reduction due to using these forms is obtained at higher floors and at balcony of 2 m depths and more. As a consequence of simulation results, it is found that the prediction of protection levels from 10th to 15th floor can be calculated from an empirical equation.     

An experimental study on the effect of rolling shutters and shutter boxes on the airborne sound insulation of windows

The façade of a room is usually composed of different construction elements, one of which is the window. This fulfils both an aesthetic function and closes the wall opening. In order to improve thermal behaviour and control solar radiation, the window is fitted with different protection features, such as the shutter. In climate zones with many hours of sunlight, windows in residential buildings commonly incorporate a rolling shutter. Traffic noise and higher standards of energy saving, comfort, durability and sustainability in buildings means that windows now have to comply with stricter requirements, including their sound insulation from airborne noise. This work contains a summary of studies carried out on the sound insulation from airborne noise in several types of windows (double side-hung casement and double horizontal sliding sash) with built-on shutter and prefabricated box. For each type of window, an analysis was made of the effects of the interior finishings in the shutter box, the shutter position (whether fully retracted or extended) and the weighted sound reduction index of windows for traffic noise in accordance with EN ISO 717-1.     

Context sensitive noise impact mapping

Apartments that are exposed to the same level of road traffic noise on front of the most exposed façade often have very different neighbourhood soundscapes. In the first part of this paper, a neighbourhood soundscape adjusted exposure indicator, NAL_den, is derived. NAL_den-values are designed to be used as input to traditional exposure-effect relationships to improve annoyance impact estimates. In the second part, generic spatial procedures are developed and implemented. These produce map presentations in the form of contiguous neighbourhood quality areas. The quality of each neighbourhood is determined from the predicted annoyance impacts for residents. Noise impact maps provide experts, politicians, and the public with high-level impact visualizations of condensed status, “what-if” and scenario information. Results and illustrations are based on data from the Norwegian socio-environmental survey database, and a comprehensive national noise mapping effort. The methodology should work well for mapping Europe’s “black” and “grey” areas.